World

This Winter Wasn't Nearly as Cold as You Think, Feds Say

By the imprecise measure of human perception, this winter was a brutal one across much of the central and eastern United States. Several bouts of extreme cold and snow struck from Chicago to Kansas City, and eastward to Washington, New York and Boston. At times the frigid weather — related in part to wobbles in the polar vortex and deep dips in jet stream winds — extended all the way to the Gulf Coast.

But according to new data released Thursday, the winter of 2013-14 (meteorological winter is defined as December through February) was not historically cold for the country as a whole. Instead, nationally speaking, this winter was an example of how the long-term increase in average temperatures, which is due in part to emissions of manmade greenhouse gases, is warping our sense of what a frigid winter looks and feels like.

Nationally, it was the 34th coldest winter, as unusually warm weather west of the Rocky Mountains offset the cold temperatures in the Midwest and the East. For the lower 48 states (the U.S. minus Alaska and Hawaii), it was the coldest winter since 2009-10, and colder than most of the winters of the past 20 years — and not, as one prominent media outlet stated, the coldest winter of the past 100 years.

Not a single state set a record for its coldest winter on record, although seven states in the Midwest did make it into their top 10 coldest. In contrast, one state, California, had its warmest winter on record, with drought conditions worsening and expanding throughout the season, likely paving the way for a perilous wildfire season ahead with water management challenges.

So, if this winter wasn’t all too cold nationally, and even the coldest spots did not obliterate their historical cold records, why is it that it felt so cold? The primary reason is likely the fact that winters have been warming significantly across the lower 48 states during the past century, particularly since 1970, according to data from NOAA’s National Climatic Data Center.

Long-term trends in average winter (December through February) temperatures across the lower 48 states.

Image: NOAA

As the above map shows, the warming has been especially pronounced in some of the coldest parts of the country, such as the Upper Midwest and the Northeast. This warming is consistent with global trends caused in large part by manmade emissions of greenhouse gases.

There was one region where the frigid temperatures did rival historical cold outbreaks, and that was the Midwest. But even there, few locations had their all-time coldest winters, despite frequently bone-chilling temperatures. Many spots, however, did set some cold temperature records, such as records for the longest streaks of temperatures below certain thresholds. Even when viewed in this light, though, this winter did not blow away the winters that one hears about from family elders, when pipes froze and people had to skate to work or school uphill, against the wind, as their eyelashes froze solid.

Mainly, though, this winter rivaled — but did not beat — the historically cold winters that occurred in the early 1980s, and mid-to-late 1970s. That means that if you're young (say, around 30-years-old) and living in Michigan or Illinois, this was probably the coldest and snowiest winter you've experienced. However, it wasn't the most severe winter on record, since instrument records extend back all the way to the late 19th century.

The Midwest tends to experience the purest, most bone-chilling cold because it is the first place to experience the Arctic air masses as they invaded the U.S. Such cold outbreaks tend to ease slightly as they shift south and east, especially if they move over ground that is not covered in snow.

As this graphic from the National Oceanic and Atmospheric Administration (NOAA) shows, Chicago had an unusually cold winter, with temperatures frequently falling well below average.

This graphic shows the day-by-day temperature for the season, in a bar format. Each day's high temperature and low temperature define the size and placement of that day's bar. The 1981-2010 normal values, taken from official Normals data, is displayed as a shaded backdrop for context. Note how frequently the bars fall below the shaded backdrop, indicating colder than average temperatures.

Image: NOAA

However, it's been colder there before.

As this second NOAA graphic shows, winters in the 1970s and 1980s had more days with low temperatures below minus-15 degrees Fahrenheit, which is the threshold NOAA scientists chose to illustrate the difference between a cold winter and a frigid one.

This shows how the coldest air of winter 2013-14 compares with cold outbreaks from Chicago's history, by comparing the number of days with temperatures as cold or colder than the threshold occurred each year. The threshold here is days with minimum temperatures at or below minus-15 degrees Fahrenheit. Many other winters had more days with such extreme cold.

Image: NOAA

The Midwest had an especially cold February, with temperatures that dipped to the coldest readings seen since 1979 in some locations. In Wisconsin, monthly average statewide temperatures were the coldest since 1936.

In several cities, this winter ranked among the top 10 coldest such seasons, including in Indianapolis, where it was the 5th-coldest, and Green Bay, Wisc., where it was the second-coldest. But no location listed in NOAA's report had a coldest winter on record.

In contrast, six cities in the West, including San Francisco and Las Vegas, had their warmest winters on record.

This winter was unusually snowy in Chicago, with Midway Airport now standing at its 3rd-snowiest year on record, with 85.2 inches so far. This is just 4.5 inches shy of the all-time seasonal record of 89.7 inches, set in 1962. Given that it can snow in Chicago into the month of April, it’s conceivable that this record will be broken this year. Detroit is currently at its second-snowiest winter on record, set in 1880-81, and this too could be eclipsed sometime during March or April if the city is hit with another significant winter storm.

Several other cities set snowfall records this winter, including Indianapolis, where 55.1 inches fell, compared to the average of 25.9 inches, and Toledo, where 84.8 inches fell, compared to the average of about 37 inches inches. Philadelphia had a record six storms that brought snowfall greater than six inches, which had never happened before since records began there in 1875.

New York City's average winter temperature for 2013-14 compared to historical data.

Image: Climate Central

Nationally, winter snow cover extent in the lower 48 states was 1.42 million square miles, according to the Rutgers University Snow Lab. This was 170,000 square miles above the 1981-2010 average, making it the 10th largest season snow cover extent since such records began in 1966.

Many people in the East would be surprised to learn that this winter was not all that cold, historically speaking. In New York City, for example, December through February temperatures ranked right in the middle of the historical range, with similar stories in Washington, Philadelphia and Boston.

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